Technical Field
The instant disclosure relates to a light-emitting device diagnostic circuit, in particular, to a diagnostic circuit for detecting abnormal light-emitting device of the printer head for the printing devices.
Related Art
An light emitting diode (LED) is a light source based on the conversion of electrical energy to light energy. An LED's advantages include high efficiency and long service life, which allow the LED to be widely used amongst various fields. In addition to being used in large quantities for everyday activities, in recent years, LEDs are also making presence in 3C (computers/communications/consumers), products and small home appliances, such as LED screens, LED lamps, etc. Furthermore, some manufactures have applied LED technology to printers; for example, the replacement of the laser printer head by the LED printer head.
LED printers and laser printers have similar operating principles; specifically both types of printer adopt optical technology to convert digital data into light data. The light-sensitive drum then attracts the toner to make printed documents. However, LED printers are more advantageous than laser printers, since LED printers omit complicated optical structures, only using simple LED arrays cooperating with optical components. Consequently, LED printers save more space, in addition to having low distortion rate and high precision. However, one issue associated with LED printers is that if any LED in the LED printer head's array is abnormal or damaged, the printing quality will be adversely affected, and the abnormal part must be replaced. Consequently, to ensure the LEDs' light emitting quality and the printer performance, the testing of each LED of the printer head is critical. The conventional testing method involves supplying voltage directly to the LEDs, and inspecting the emitting status to check for any abnormality. However, whether by supplying voltages section-by-section or all at once, such an inspection method is relatively inconvenient.